1. Unprovable hypothesis that since galaxies and galactic clusters don't have enough mass to produce enough gravity to spin the way they do, that there thus must be invisible matter hiding that's making it all work.

2. The observation of the universe sometimes fails to follow the known laws of physics, so instead of theorizing that there must be more laws we've yet to discover, scientists have instead decided to push forward the idea that invisible masses must exist, and thus explain away the discrepancies and gaps in our knowledge.

3. Science akin to religion in that nothing at all proves it, but lots of people believe it because it explains something that was hitherto before difficult to understand.

4. Theory regarding matter and gravity that seems to make sense of Newtonian physics when it fails us, but in doing so introduces a concept that is completely ludicrous.

5. Alternative hypothesis to how the universe works to the much more logical MOND theory, or variations thereof.

6. An example of lazy science.

7. The greatest example of how extremely intelligent people can at times be completely clueless, lacking in all common sense.

I don't understand this crap, makes my head hurt, there must be Dark Matter, or something.

That astrophysicist over there, he can't understand how shit works so he's decided he's gonna pull some old bullshit theory out his ass and see if he can prove its true. He calls it Dark Matter cause its like all invisible 'n shit.

Aliens beamed me up yo, just sos they could like laugh at all a us for this Dark Matter bullshit.

I'm done with reason, from now on I believe in Big Foot, Vampires, honest politicians, and Dark Matter yo!

A substance excreted by nibblonians. It is the fuel source for rocket ships in the year 3000. Among the many astounding properties of dark matter is its incredible density, such that every pound of dark matter weighs over 1000 pounds.

Cop 1: Smells like a 289 in progress.
Cop 2: Failure to scoop, aww yeahh.
Fry (attempting to lift the dark matter poop): Wait, I'm trying! It weighs as much as a thousand suns!

There is an unfortunate situation: your bong has no glass screen and some of the budha inevitably pulls through. worry not. allthough some may fall to the bong water, much sticks to the the resin in the stem of your bowl: this is dark matter. Hallelujah, your not out quite yet!